PTH and secondary hyperparathyroidism: This is exactly what we see in children with burns, with low PTH levels, low blood ionized calcium, and high urinary calcium.13 Conversely, with primary or secondary hyperparathyroidism, there is a downregulation of the calcium-sensing receptor, indicating that it takes higher than normal concentrations of circulating calcium to turn off the signal for PTH secretion, resulting in hypercalcemia and hyperparathyroidism.